Process for reducing iron iii oxide contained in calcinated clay
By using hydrogen and carbon monoxide reducing gases to reduce calcined clay in a reduction reactor and a cooling reactor, the problems of high cost and high temperature reduction in existing technologies are solved, and low-cost, low-environmental-impact gray calcined clay production is achieved.
Patent Information
- Application Number
- CN202580011236.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-01-23
- Filing Date
- 2025-01-22
- Publication Date
- 2026-08-25
AI Technical Summary
Existing technologies require large amounts of liquid reducing agents, such as diesel fuel, to reduce iron III oxides contained in calcined clay, resulting in high costs and significant environmental impact. In addition, the reduction reaction must be carried out at high temperatures, which affects energy efficiency.
The reduction of iron III oxides is achieved by contacting calcined clay with a reducing gas containing hydrogen and/or carbon monoxide through a combination system of a reduction reactor and a cooling reactor, thereby reducing the amount of reducing agent used and optimizing energy consumption.
It effectively produces gray calcined clay, reduces the amount of reducing agent used and environmental impact, while improving energy efficiency and meeting the color requirements of cement production.
Smart Images
Figure CN122641592A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for reducing iron III oxides contained in calcined clay. Specifically, this invention relates to a method for reducing iron III oxides contained in calcined clay intended for use in the production of binders with desired color properties. Background Technology
[0002] The following content focuses in particular on the reduction of iron III oxides contained in calcined clay intended for use in cement manufacturing, although calcined clay can also be used for other applications.
[0003] In cement manufacturing, a type of calcining material called clinker is used, which is produced from minerals whose basic component is calcium carbonate.
[0004] Clinker is obtained from raw materials consisting of a mixture of minerals, particularly clay as a source of aluminosilicates and limestone as a source of calcium carbonate. These minerals are sequentially mixed, dried, ground, preheated, and decarburized, and then fired and partially melted in a rotary kiln at a temperature of about 1500°C, after which the resulting clinker is cooled.
[0005] Cement is obtained by finely grinding a mixture that consists mainly of clinker.
[0006] In the clinker manufacturing process, in addition to CO2 emissions from the combustion of the fuel used, calcium carbonate, mainly derived from limestone, is decarbonized to obtain lime. The lime then recombines with oxides of silicon, aluminum, and iron in a rotary kiln to form clinker. This decarbonization stage releases a large amount of carbon dioxide into the atmosphere.
[0007] National laws regarding carbon dioxide emissions are becoming stricter, forcing operating companies to reduce their emissions.
[0008] In addition to clinker, cement also contains gypsum, which regulates the setting time of mortar and concrete. Cement also increasingly contains a growing proportion of materials, often referred to as "cement admixtures," which are used to replace clinker in order to reduce the environmental impact and cost of cement manufacturing.
[0009] For example, the most commonly used materials to replace clinker are limestone, blast furnace slag, fly ash from coal-fired power plants, and natural volcanic ash.
[0010] Apart from limestone used solely as filler, these clinker substitutes possess pozzolanic reactivity, enabling them to participate in the hydraulic setting reaction. This pozzolanic reactivity helps maintain the desired mechanical properties of mortar and concrete when the proportion of clinker is reduced.
[0011] Clay, especially clay containing kaolinite, acquires pozzolanic reactivity upon calcination, thus becoming an excellent clinker substitute in cement manufacturing. It is also known as "artificial pozzolanic."
[0012] Unlike clinker production, calcined clay production emits very little CO2.
[0013] Cement with desired properties can be produced by wisely reducing the proportion of clinker while increasing the proportion of calcined clay.
[0014] Clay has a pale reddish hue due to its content of iron III oxide (Fe2O3). Adding calcined clay to cement without treatment will result in cement with a pinkish tint.
[0015] Both cement producers and end users prefer gray cement.
[0016] Several methods have been implemented to alter the natural color of calcined clay and turn it gray.
[0017] These technologies include a method that involves chemically reacting iron III oxide molecules (Fe₂O₃) to obtain iron(III) oxide (Fe₃O₄). This is a redox reaction. After the initial clay calcination step, the clay is sent to a reduction zone where a liquid reducing agent, particularly diesel fuel, is injected directly onto the clay. The diesel fuel creates conditions that allow iron III oxide to be reduced to iron(III) oxide and iron II oxide (FeO).
[0018] Although this method produces gray clay, it has two main drawbacks:
[0019] - Injecting large amounts of diesel fuel to reduce iron III oxides affects both clay costs and the environment.
[0020] The reduction reaction must be carried out at high temperatures, which affects the energy efficiency of the method.
[0021] The present invention is particularly intended to overcome these shortcomings. Summary of the Invention
[0022] Therefore, a method for reducing iron III oxides contained in calcined clay is first proposed, which includes the following steps:
[0023] Step a) involves introducing calcined clay containing iron III oxides into a reduction reactor.
[0024] Step b) of reducing calcined clay in a reduction reactor includes operation O1) contacting the calcined clay with a reducing gas containing hydrogen atoms to obtain reduced clay particles containing iron II oxide and / or iron(III) oxide, and a stream of reducing gas to be treated.
[0025] Step c) involves suspending the reduced clay particles in a cooling gas stream in a cooling reactor to cool the reduced clay particles.
[0026] Step d) involves mixing the reduced clay particles with at least a portion of the reducing gas stream to be treated, to obtain a mixture after steps c) and d), the mixture comprising:
[0027] -Cooled, reduced clay particles,
[0028] - at least a portion of the reducing gas stream to be processed, and
[0029] -Cooling gas flow,
[0030] Step e) involves separating the mixture to obtain a gas stream separated from the cooled, reduced clay particles.
[0031] Step f) involves separating at least a portion of the gas stream from the reduced clay particles to obtain a cooling gas, and...
[0032] Step i) involves introducing cooling gas into the cooling reactor such that the cooling gas flow is at least partially composed of the cooling gas obtained in step f), and step i) results in the formation of a cooling loop.
[0033] This method advantageously allows for the production of gray clay using a small amount of reducing agent, significantly less than when using liquid reducing agents. Furthermore, this method improves the reduction of iron(III) oxides because the contact between the calcined clay and the reducing gas is maintained for a longer period during each step of the method.
[0034] Various additional features can be provided individually or in combination:
[0035] - The reducing gas contains hydrogen and / or carbon monoxide;
[0036] - The amount of reactants contained in the reducing gas is between 0.1 moles and 2 moles per mole of iron III oxide contained in the introduced calcined clay, preferably between 0.3 moles and 0.7 moles;
[0037] - The method further includes a step g) of cooling at least a portion of the cooled reduced clay particles obtained by separation step e), wherein cooling step g) includes an operation O2) of contacting the cooled reduced clay particles with the cooling gas obtained by cooling step f) to obtain a gaseous suspension of the cooled reduced clay particles.
[0038] -The method further includes, after cooling step f), an operation O3) to extract a portion of the cooling gas from the cooling circuit to maintain negative pressure in the cooling circuit;
[0039] -The method also includes, after the extraction operation O3), the operation O4) sending the extracted portion of the cooling gas to the calcining furnace;
[0040] - The method also includes operation O5) of supplying heat energy and / or fuel to the cooling circuit to consume oxygen contained in the gas stream circulating in the cooling circuit, operation O5) being performed prior to cooling step f);
[0041] -The method further includes step h) of separating the gaseous suspension of cooled, reduced clay particles to obtain:
[0042] - Cooling gas, containing hydrogen atoms, separates from the cooled, reduced clay particles.
[0043] -Cooled, reduced clay particles,
[0044] - The cooling gas introduced into the cooling reactor during step i) consists of the cooling gas obtained in step h) separated from the cooled and reduced clay particles;
[0045] Secondly, it is proposed to use the above-mentioned reduction method to produce calcined clay with desired color characteristics.
[0046] Third, a facility for reducing iron III oxides contained in calcined clay is proposed, the facility being configured to perform the method described above and comprising:
[0047] - A reduction reactor configured to contact calcined clay with a reducing gas containing hydrogen atoms. The reduction reactor includes an outlet for reduced clay particles containing iron II oxide and / or iron(III) oxide and an outlet for the reducing gas stream to be treated.
[0048] - A cooling reactor in which reduced clay particles are suspended in a stream of cooling gas, and a stream of reducing gas to be treated is optionally injected therein. The cooling reactor includes an outlet through which a mixture containing the following substances is discharged:
[0049] -Cooled, reduced clay particles,
[0050] - Cooling gas flow, and
[0051] - Optionally, at least a portion of the reducing gas stream to be treated,
[0052] - A first gas / particle separation device configured to separate cooled, reduced clay particles from a mixture discharged from a cooled reactor, the first gas / particle separation device comprising:
[0053] • An inlet configured to receive the mixture.
[0054] • A gas outlet for separating the gas stream from the cooled, reduced clay particles, and
[0055] • Particle outlet for cooling reduced clay particles,
[0056] - A cooling device configured to cool at least a portion of a gas stream separated from cooled reduced clay particles, the cooling device including an outlet for cooling the gas.
[0057] - A device for introducing cooling gas into a cooling reactor, such that the cooling gas flow consists at least in part of the cooling gas leaving the cooling device, thereby forming a cooling loop.
[0058] Various additional features can be provided individually or in combination:
[0059] - The facility also includes a ventilation system for cooling gases, which is arranged between the cooling unit and the cooling reactor to ensure the circulation of gas flow in the cooling loop;
[0060] - The facility also includes means for supplying heat and / or fuel to the cooling circuit to consume the oxygen contained in the gas stream circulating in the cooling circuit, the supply means being arranged between the first gas / particle separator and the cooling unit.
[0061] - The facility also includes a second cooling device configured to further cool at least a portion of the cooled, reduced clay particles exiting the first gas / particle separation unit, the second cooling device comprising:
[0062] • A gas inlet for at least a portion of the cooling gas, wherein the gas inlet of the second cooling device is connected to the outlet of the first cooling device.
[0063] • The material inlet for at least a portion of the cooled, reduced clay particles exiting the first gas / particle separator, and
[0064] - An outlet for cooling the gaseous suspension of reduced clay particles;
[0065] - The facility also includes a second gas / particle separation unit configured to separate at least a portion of the cooled particles from a gaseous suspension of cooled, reduced clay particles. The second gas / particle separation unit includes:
[0066] -A gas outlet for separating the cooling gas from the cooled, reduced clay particles, and
[0067] - Particle outlet for cooling reduced clay particles,
[0068] The gas outlet of the second gas / particle separator is connected to a device for introducing cooling gas into the cooling reactor. Attached Figure Description
[0069] Further features, details, and advantages will become clear from the following detailed description and analysis of the accompanying drawings, in which:
[0070] [ Figure 1 [Illustration] is a schematic diagram of a facility according to an embodiment of the present invention, and
[0071] [ Figure 2 [Illustration] is a schematic diagram of a facility according to an embodiment of the present invention.
[0072] The accompanying drawings and the following description primarily contain elements that define the nature of this disclosure. Therefore, they can be used not only to aid in understanding this disclosure but also, where appropriate, to help define it.
[0073] More specifically, in the following text, without limiting the invention, Figure 1 and Figure 2 Each of the two facilities shown (which are facilities for reducing iron III oxides contained in calcined clay according to two different embodiments) is considered to constitute part of the overall binder manufacturing method (e.g., cement manufacturing method). Specifically, the reduced calcined clay is considered to be intended for use in cement manufacturing as a partial substitute for clinker, as an active filler directly incorporated into concrete, or as a component of geopolymer cement.
[0074] Calcined clay is produced by calcining raw clay containing iron III oxides in a calcining furnace (not shown in the attached figure) in step a0).
[0075] For the purposes of this invention, "raw clay" refers to any type of clay mineral, including shale.
[0076] Preferably, the raw clay contains kaolinite.
[0077] Preferably, before the calcination step a0), the raw clay is ground and dried, then preheated in a preheater, and then fed into the calcination furnace. Generally, the calcination furnace includes a combustion chamber that generates hot gases and a calcination reactor in which the clay from the preheater comes into contact with the hot gases for calcination. The calcination reaction is preferably carried out in an oxidizing atmosphere under conditions of excess oxidant. The flue gas outlet of the calcination furnace can be connected to the preheater and optionally to other devices commonly used in general binder manufacturing processes, such as a raw clay grinding and drying unit and one or more flue gas pollution control and filtration devices.
[0078] To activate the pozzolanic properties of calcined clay and make it suitable for use in cement production, step a0) of calcining raw clay is carried out at a temperature below 950°C. Calcination step a0) is carried out under stoichiometric or oxidizing conditions.
[0079] Next, step a) is performed whereby calcined clay is introduced into the reduction reactor 100, particularly through the material inlet 1002 of the reduction reactor 100. It should be noted that the temperature of the calcined clay introduced in step a) is between 600°C and 950°C, or preferably between 750°C and 850°C. The calcined clay is then guided from the calcining furnace to the material inlet 1002 of the reduction reactor 100. The reduction reactor 100 is preferably a static reactor, a fluidized bed reactor, or a rotary reactor. The reduced clay particles containing iron II oxide and / or iron(II) oxide leave the reduction reactor 100 through the material outlet 1006, and the reducing gas stream to be treated leaves through the gas outlet 1008.
[0080] For the purposes of this patent application, "reducing gas flow to be processed" means the gas flow that leaves the reduction reactor and is fed into the cooling circuit to pass through its components.
[0081] The calcined clay is preferably held in the reduction reactor 100 under optimal reduction conditions for a residence time of greater than 10 seconds and at most 10 minutes, preferably at most 5 minutes, or even at most 2 minutes. The reduction reactor 100 particularly includes a reducing gas inlet 1004 through which reducing gas is injected. Therefore, in subsequent steps, step b) of reducing the calcined clay is carried out in the reduction reactor 100. This reduction step b) particularly includes an operation O1) of contacting the calcined clay with the reducing gas injected into the reduction reactor 100, the reducing gas containing hydrogen atoms. This enables the reduction of at least a portion of the iron III oxides in the calcined clay to Fe3O4 (iron tetroxide) and / or FeO (iron II oxides).
[0082] A reducing gas containing hydrogen atoms enables the reduction of iron III oxides according to the following reaction to primarily obtain iron(III) oxide and optionally iron II oxide FeO:
[0083]
[0084] Furthermore, according to the following reaction equation, carbon monoxide reacts with iron III oxide in the presence of carbon monoxide:
[0085]
[0086] Using a reducing gas containing hydrogen atoms instead of diesel fuel or any other liquid fuel as the reducing agent significantly reduces the amount of reducing agent used during reduction step b). Therefore, gray calcined clay is produced at a significantly lower cost. Furthermore, the environmental impact of producing gray calcined clay is reduced.
[0087] Advantageously, the reducing gas contains hydrogen and / or carbon monoxide.
[0088] Even more advantageously, the reducing gas contains:
[0089] -A mixture containing hydrogen (H2) and carbon monoxide (CO), or
[0090] - Hydrogen gas (H2).
[0091] For example, hydrogen (H2) and carbon monoxide (CO) can be obtained directly from the storage device or generated by the dissociation of hydrocarbons in a reactor designed to produce reducing gases. The dedicated reactor can be an endothermic or exothermic gas generator from which the reducing gas injected into the reduction reactor 100 is obtained.
[0092] It should be noted that the aforementioned reducing gas can be mixed with other gases, mainly nitrogen and / or carbon dioxide and / or gaseous hydrocarbons of the general formula CnHm that have not yet dissociated into hydrogen (H2) and carbon monoxide (CO).
[0093] Advantageously, the amount of reducing gas injected into the reduction reactor 100 and in contact with the calcined clay is substantially between 0.1 and 2 moles of reactant per mole of iron III oxide contained in the introduced calcined clay. By adhering to this amount, calcined clay with the desired gray color is obtained while minimizing gas input, thereby reducing clay production costs and environmental impact. Preferably, the amount of reducing gas injected into the reduction reactor 100 and in contact with the calcined clay corresponds to an amount of reactant substantially between 0.3 and 0.7 moles per mole of iron III oxide contained in the introduced calcined clay. This range enables efficient reduction reactions while optimizing the energy consumption required to produce the reducing gas.
[0094] At the end of reduction step b), the following substances are obtained: on the one hand, reduced clay particles containing iron II oxide and / or iron(III) oxide, and on the other hand, a stream of reducing gas to be treated. The reduced clay particles leave the reduction reactor through material outlet 1006, and the stream of reducing gas to be treated leaves through gas outlet 1008.
[0095] For the purposes of this patent application, "reduced clay particles" refers to calcined clay particles that have undergone a reduction reaction in a reduction reactor and have achieved the desired color.
[0096] The reduced clay particles are then fed via a fluid conduit to the material inlet 1106 of the cooling reactor 110. During suspension step c), the reduced clay particles are suspended in a cooling gas stream passing through the cooling reactor 110. Specifically, the cooling gas stream passes from the gas inlet 1102 through the cooling reactor 110 to the outlet 1104. This cools the reduced clay particles leaving the reduction reactor 100 and being introduced into the cooling reactor 110. A mixture containing cooled reduced clay particles and the cooling gas stream is thus obtained.
[0097] Preferably, at least a portion of the reducing gas stream leaving the reduction reactor 100 is also introduced into the cooling reactor 110 through inlet 1108. A mixing step d) then takes place in the cooling reactor 110. Therefore, the aforementioned mixture also contains the aforementioned at least a portion of the reducing gas stream introduced into the cooling reactor 110. Figure 1 and Figure 2 In the illustrated embodiment, the entire stream of reducing gas to be treated is introduced into the cooling reactor 110. However, only a portion of the stream of reducing gas to be treated may be introduced into it.
[0098] In a variant embodiment not shown in the accompanying drawings, the reducing gas stream to be treated is mixed with the clay particles leaving the reducing reactor 100 before the clay particles are introduced into the cooling reactor 110. In this case, the reduced clay particles are introduced into the cooling reactor 110 in the form of a mixture containing the reduced clay particles and the reducing gas stream to be treated.
[0099] In another variant embodiment not shown in the accompanying drawings, the reducing gas stream to be treated is mixed with the clay particles leaving the reducing reactor 100 after a mixture containing cooled, reduced clay particles and a cooling gas stream has been formed, i.e., after the mixture containing cooled, reduced clay particles and a cooling gas stream leaves the cooling reactor 110.
[0100] exist Figure 1 and Figure 2 In the illustrated embodiment, cooling gas is introduced into cooling reactor 110 through inlet 1102, and a mixture containing cooled reduced clay particles, cooling gas stream, and reduced gas stream to be treated exits cooling reactor 110 through outlet 1104.
[0101] The mixture is then fed via a fluid conduit to the material inlet 1202 of a first gas / particle separator 120, which is configured to separate cooled, reduced clay particles from the gas stream during separation step e).
[0102] At the end of separation step e), the following substances are obtained:
[0103] - A gas stream separated from the cooled, reduced clay particles, exiting through the gas outlet 1204 of the first gas / particle separator 120, and
[0104] - Cooled, reduced clay particles exit through the material outlet 1206 of the first gas / particle separator 120.
[0105] Preferably, the first gas / particle separation device 120 is a cyclone separator.
[0106] After separation step e), the gas stream that has separated from the cooled, reduced clay particles and exited the first gas / particle separation device 110 (e.g., through its upper outlet) is directly or indirectly delivered to the first cooling device 140 and fluidly connected thereto via a conduit.
[0107] Therefore, step f) involves separating the gas stream from the reduced clay particles via the first cooling device 140.
[0108] The first cooling device 140 includes, on the one hand, an inlet 1402, which is directly or indirectly fluidly connected to the upper outlet or gas outlet 1204 of the first gas / particle separator 120, and on the other hand, an outlet 1404 through which the cooling gas exits. The first cooling device 140 is thus configured to obtain cooling gas. For example, the first cooling device 140 may be a waste heat boiler or an air cooler.
[0109] Advantageously, during step f), the temperature of the reducing gas stream is lowered to below a threshold temperature between 200°C and 450°C during the cooling of the gas stream separated from the cooled reduced clay particles. This is indirect cooling because the gas stream separated from the cooled reduced clay particles does not come into direct contact with the cooling fluid. Therefore, the ventilation device 150 can be connected to the outlet 1404 of the first cooling device 140 without being damaged by the overheated gas stream. The ventilation device 150 promotes the circulation of the gas stream through the aforementioned facility components and those described below. Furthermore, since the gas stream has been cooled during cooling step f), a wide range of ventilation devices 150 suitable for such gas stream temperatures can be used.
[0110] according to[ Figure 1 The embodiment shown in the figure involves step i) introducing cooling gas into the cooling reactor 110. This allows at least partial or complete flow of cooling gas into the cooling reactor 110 through inlet 1102. Figure 1The mixture consists of the cooling gas obtained in step f). It should be noted that the introduction step i) results in the formation of a cooling circuit. The cooled, reduced clay particles obtained in separation step e) and then exiting through the material outlet 1206 of the first gas / particle separator 120 are recovered in this embodiment and optionally stored in a suitable storage device. Advantageously, the recovered cooled, reduced clay particles are at a temperature between 200°C and 600°C, preferably between 350°C and 500°C.
[0111] However, to optimize the cooling of reduced clay particles, and especially to improve the energy efficiency of cooling reduced clay particles, cooling should be carried out in multiple stages, for example, using two separate cooling devices 140 and 170 in two stages. Multi-step cooling allows for energy optimization of the entire reduction process.
[0112] Therefore, according to [ Figure 2 In the embodiment shown, before step i) of introducing cooling gas into the cooling reactor 110, the cooling gas exiting the first cooling device 140 is used to cool the cooled, reduced clay particles exiting through the material outlet 1206 of the first gas / particle separator 120. Advantageously, step g) of cooling the cooled, reduced clay particles exiting through the material outlet 1206 of the first gas / particle separator 120 is then performed.
[0113] The cooling step g) is performed using a second cooling device 170, which is configured to further cool the cooled, reduced clay particles already cooled in the cooling reactor 110. This cooling step g) of the reduced clay particles includes contacting the cooled, reduced clay particles with cooling gas exiting the first cooling device 140 (O2). This also allows for a further reduction in temperature of the cooled, reduced clay particles in an economical and environmentally friendly manner to prevent re-oxidation of iron II oxides and / or magnetite in the reduced clay particles exiting the reduction reactor 100 through its outlet 1006.
[0114] like[ Figure 2As shown, the second cooling device 170 includes a gas inlet 1702 through which cooling gas is introduced. The gas inlet 1702 is indirectly connected to the outlet 1404 of the first cooling device 140 via a ventilation device 150. It also includes a material inlet 1704, which is connected to the lower outlet or material outlet 1206 of the first gas / particle separator 120. The cooled, reduced clay particles obtained in separation step e) are introduced through this material inlet. The second cooling device 170 also includes an outlet 1706 through which the gaseous suspension of the cooled, reduced clay particles is discharged. It should be noted that during the cooling step g), the cooling gas is heated upon contact with the cooled, reduced clay particles, which are hotter than the cooling gas.
[0115] Advantageously, the operation of O2 is carried out by bringing the cooling gas into direct contact with the cooled, reduced clay particles, provided that the cooling gas contains less than 2% oxygen by volume.
[0116] Advantageously, during the cooling step (g) of the cooled reduced clay particles, the temperature of the cooled reduced clay particles is lowered to below a threshold temperature between 200°C and 600°C, preferably between 350°C and 500°C, thereby preventing the re-oxidation of iron II oxides and / or iron tetroxide during subsequent steps that expose the reduced calcined clay to air (e.g., during final air cooling and during processing and storage).
[0117] Advantageously, step h) of separating the gaseous suspension of cooled reduced clay particles is performed after step g) of cooling the reduced clay particles. This step h) of separating the gaseous suspension of cooled reduced clay particles is performed using a second gas / particle separator 180, which is configured to separate the cooled particles from the gaseous suspension of cooled reduced clay particles.
[0118] The gaseous suspension of cooled particles is then introduced into a second gas / particle separator 180 through an inlet 1802 connected to an outlet 1706 of the second cooling device 170. The second gas / particle separator 180 further includes, on the one hand, a gas outlet 1806 for cooling gas containing hydrogen atoms and separated from the cooled, reduced clay particles, and on the other hand, a particle outlet 1804 for the cooled, reduced clay particles. The second gas / particle separator 180 can be, for example, of the same type as the first gas / particle separator 120. The cooled, reduced clay particles discharged through the particle outlet 1804 of the second gas / particle separator 180 can be cooled during a final cooling step (e.g., using air) to obtain cooled, reduced clay particles at a temperature between 100°C and 150°C. At this temperature, the particles can be easily stored and packaged. The particles can then be mixed, for example, with clinker intended for cement production. This application makes it possible to produce gray cement by reducing the proportion of clinker in the cement and replacing it with calcined clay.
[0119] Advantageously, step i) is now performed whereby the cooling gas, separated from the cooled and reduced clay particles, leaving the second gas / particle separator 180 is introduced into the cooling reactor 110. Thus, the cooling gas that comes into contact with the calcined clay during operation O1) consists at least in part of a gaseous suspension of the cooled and reduced clay particles.
[0120] It should be noted that a cooling circuit is formed by introducing cooling gas, which is separated from the cooled and reduced clay particles, into the cooling reactor 110 through the gas inlet 1102.
[0121] In the presence of such a cooling circuit, according to Figure 1 and Figure 2 In any of the embodiments shown, it is advantageous to ensure thermal and pressure balance so that the cooling circuit remains stable. In particular, the reduction circuit is preferably maintained in a reducing atmosphere, and the flow rate of the circulating gas stream is greater than the flow rate at which at least a portion of the reducing gas stream to be treated is injected into the cooling reactor 110.
[0122] Therefore, after step f), which involves cooling at least a portion of the gas stream separated from the reduced clay particles, it is advantageous to perform an operation O3) to extract a portion of the cooling gas from the cooling circuit to maintain the pressure in the cooling circuit below ambient pressure, i.e., to maintain a negative pressure in the cooling circuit. Performing such extraction operation O3) also makes it possible to compensate for the gas volume introduced into the cooling circuit, particularly when reducing gas is injected through the reducing gas inlet 1004 of the reduction reactor 100, when calcined clay is introduced into the reduction reactor 100 through the material inlet 1002 in step a), and when leakage enters the cooling circuit through any leak point in the duct or equipment.
[0123] During operation (O2), the flow rate of a portion of the cooling gas drawn from the cooling circuit is regulated using valve 160 in order to maintain a constant negative pressure in the circuit.
[0124] Preferably, valve 160 is configured to draw cooling gas at the outlet of ventilation device 150 in the direction of gas flow.
[0125] Next, optionally, a portion of the extracted cooling gas is sent to a calcining furnace for obtaining calcined clay before it is introduced into the reduction reactor 100 (O4). Thus, the extracted cooling gas is incinerated, and the energy released by the combustion of gases contained in the cooling gas (such as hydrogen, carbon monoxide, and gaseous hydrocarbons) is recovered.
[0126] Furthermore, it is advantageous to perform the operation of supplying heat energy and / or fuel to the cooling circuit (O5). This supply is localized within the cooling circuit and is carried out on demand. This prevents an increase in oxygen in the gas flow circulating in the cooling circuit and also prevents the reduced calcined clay from turning from gray to red.
[0127] Furthermore, such operation of supplying heat energy and / or fuel (O5) allows for the consumption of oxygen contained in the gas stream circulating in the cooling circuit and introduced primarily by air leakage. Advantageously, as Figure 1 and Figure 2 As shown, the facility includes a supply device 130 for supplying heat and / or fuel to the cooling circuit, the supply device being arranged between the first gas / particle separator 120 and the cooling device 140. Preferably, the outlet 1204 of the first gas / particle separator 120 is connected to the inlet 1302 of the supply device 130, and the outlet 1304 of the supply device 130 is connected to the inlet 1402 of the first cooling device 140. It should be noted that in [ Figure 1 The fuel quantity introduced into the supply device 130 in the embodiment shown is greater than [ Figure 2The amounts in the embodiment shown are as follows. For example, heat input in the form of flame or electric heating, or optional additional fuel supply, is introduced into the supply device 130 through a dedicated inlet 1306 to raise the temperature of the cooling gas, thereby consuming the oxygen present in the gas stream by reacting with carbon monoxide (CO) and hydrogen (H2) present in the cooling gas. Thus, the oxygen present in the gas stream circulating through the cooling loop is consumed. This ensures that the volume concentration of oxygen in the cooling gas is maintained below 2%, preferably substantially equal to 0%, in order to achieve a neutral atmosphere in the cooling loop.
[0128] Preferably, the facility also includes sensors configured to continuously or intermittently measure the temperature of the gas flow circulating in the cooling circuit, as well as the concentrations of oxygen, hydrogen, and carbon monoxide. Using such sensors makes it particularly possible to monitor the oxygen content in the cooling circuit, thereby ensuring the safety of the cooling circuit by minimizing the risk of explosion caused by the simultaneous presence of oxygen and reducing gases.
[0129] The aforementioned facilities and methods advantageously enable the production of gray clay using a small amount of reducing gas, as a portion of the reducing gas is recycled. Furthermore, the facilities and methods improve the reduction of iron III oxides because the contact between the calcined clay and the reducing gas is maintained for a longer period during certain steps of the methods performed in the aforementioned facilities.
Claims
1. A method for reducing iron III oxides contained in calcined clay, the method comprising the following steps: Step a) involves introducing calcined clay containing iron III oxides into the reduction reactor (100). Step b) of reducing the calcined clay in the reduction reactor (100) includes operation O1) of contacting the calcined clay with a reducing gas containing hydrogen atoms to obtain reduced clay particles containing iron II oxide and / or iron(III) oxide, and a stream of reducing gas to be treated. Step c) involves suspending the reduced clay particles in a cooling gas stream in a cooling reactor (110) to cool the reduced clay particles. Step d) involves mixing the reduced clay particles with at least a portion of the reducing gas stream to be treated, to obtain a mixture after steps c) and d), the mixture comprising: -Cooled, reduced clay particles, - at least a portion of the reducing gas stream to be processed, and -The cooling gas flow Step e) involves separating the mixture to obtain a gas stream separated from the cooled, reduced clay particles. Step f) involves cooling at least a portion of the gas stream separated from the cooled, reduced clay particles to obtain a cooling gas. The cooling gas is introduced into the cooling reactor (110) such that the cooling gas flow is at least partially composed of the cooling gas obtained in step f), and step i) is performed to form a cooling circuit.
2. The method according to claim 1, wherein the reducing gas comprises hydrogen and / or carbon monoxide.
3. The method according to claim 1 or claim 2, wherein the amount of reactants contained in the reducing gas is between 0.1 moles and 2 moles per mole of iron III oxide contained in the introduced calcined clay, preferably between 0.3 moles and 0.7 moles.
4. The method according to any one of claims 1 to 3, further comprising step g) cooling at least a portion of the cooled reduced clay particles obtained by separation step e), the cooling step g) comprising operation O2) contacting the cooled reduced clay particles with the cooling gas obtained by cooling step f) to obtain a gaseous suspension of the cooled reduced clay particles.
5. The method according to any one of claims 1 to 4, wherein after cooling step f), the method further includes an operation O3) of extracting a portion of the cooling gas from the cooling circuit to maintain a negative pressure in the cooling circuit.
6. The method according to claim 5, further comprising, after extraction operation O3), an operation O4 of sending the extracted portion of the cooling gas to a calcining furnace.
7. The method according to any one of claims 1 to 6, the method further comprising operation O5) supplying thermal energy and / or fuel to the cooling circuit to consume oxygen contained in the gas stream circulating in the cooling circuit, operation O5) being performed prior to cooling step f).
8. The method of claim 7, further comprising step h) of separating the gaseous suspension of cooled, reduced clay particles to obtain: • The cooling gas, containing hydrogen atoms, is separated from the cooled, reduced clay particles. • Cooled, reduced clay particles, The cooling gas introduced into the cooling reactor (110) during step i) consists of the cooling gas obtained in step h) separated from the cooled and reduced clay particles.
9. Use of the reduction method according to any one of claims 1 to 8 for producing calcined clay having desired color characteristics.
10. An apparatus for reducing iron III oxides contained in calcined clay, said apparatus being configured to carry out the method according to any one of claims 1 to 8 and comprising: - A reduction reactor (100) configured to contact calcined clay with a reducing gas containing hydrogen atoms, the reduction reactor (100) including an outlet (1006) for reduced clay particles containing iron II oxide and / or iron tetroxide and an outlet (1008) for a stream of reducing gas to be treated. - A cooling reactor (110) in which reduced clay particles are suspended in a cooling gas stream, and the reducing gas stream to be treated is optionally injected into the cooling reactor, the cooling reactor (110) including an outlet (1104) through which a mixture containing the following substances is discharged: -Cooled, reduced clay particles, -The cooling gas flow, and - Optionally, at least a portion of the reducing gas stream to be treated - A first gas / particle separation device (120), configured to separate cooled, reduced clay particles from the mixture discharged from the cooling reactor (110), the first gas / particle separation device (120) comprising: • An inlet (1202) is configured to receive the mixture. • A gas outlet (1204) for separating the gas stream from the cooled, reduced clay particles, and • Particle outlet (1206) for the cooled, reduced clay particles. - A cooling device (140) configured to cool at least a portion of the gas stream separated from the cooled reduced clay particles, the cooling device including an outlet (1404) for cooling the gas. - A means for introducing the cooling gas into the cooling reactor (110) such that the cooling gas flow consists at least in part of the cooling gas exiting the cooling device (140), thereby forming a cooling loop.
11. The facility according to claim 10, further comprising a ventilation device (150) for the cooling gas, the ventilation device being arranged between the cooling device (140) and the cooling reactor (110) to ensure circulation of the gas flow in the cooling circuit.
12. The facility according to claim 10 or claim 11, the facility further comprising a supply device (130) for supplying heat energy and / or fuel to the cooling circuit to consume oxygen contained in the gas stream circulating in the cooling circuit, the supply device (130) being arranged between the first gas / particle separator (120) and the cooling device (140).
13. The facility according to any one of claims 10 to 12, further comprising a second cooling device (170) configured to further cool at least a portion of the cooled, reduced clay particles exiting the first gas / particle separator (120), the second cooling device (170) comprising: • A gas inlet (1702) for at least a portion of the cooling gas, wherein the gas inlet (1702) of the second cooling device (170) is connected to the outlet (1404) of the first cooling device (140). • The material inlet (1704) for at least a portion of the cooled, reduced clay particles exiting the first gas / particle separator (120), and • Outlet for cooling the gaseous suspension of reduced clay particles (1706).
14. The facility of claim 13, further comprising a second gas / particle separation device (180), the second gas / particle separation device being configured to separate at least a portion of the cooled particles from the gaseous suspension of cooled, reduced clay particles, the second gas / particle separation device (170) comprising: -A gas outlet (1806) for separating the cooling gas from the cooled, reduced clay particles, and - Particle outlet (1804) for cooling reduced clay particles, the gas outlet (1806) of the second gas / particle separator (180) is connected to a means for introducing the cooling gas into the cooling reactor (110).